Concrete5

http://concrete5.org

concrete5 is a CMS framework that can power all types of websites. It is written in PHP, uses a MySQL database, and runs on many web servers. c5 is easy for site owners to use, flexible for developers to work with, and is simply the new version of our enterprise level solution that powers such sites as Lemonade.com, Indie911.com, and LewisAndClark200.org to just name a few. After years of being evil software guys, we've seen the light and have gone free and fully open source.